1. Field of the Invention
The present teaching relates to a nonaqueous electrolytic solution secondary battery. The present application claims priority to Japanese Patent Application No. 2015-217137 filed on Nov. 4, 2015, the entire contents of which are incorporated by reference in the present description.
2. Description of the Related Art
Nonaqueous electrolytic solution secondary batteries such as lithium ion secondary batteries (lithium secondary batteries) are lower in weight and higher in energy density than the conventional batteries. For this reason, in recent years, nonaqueous electrolytic solution secondary batteries have been used as the so-called portable power sources for personal computers, portable terminals, etc. and also as drive power sources for vehicles. In particular, lightweight lithium ion secondary batteries which make it possible to obtain a high energy density are expected to become increasingly popular in the future as high-output drive power sources for vehicles such as electric vehicles (EV), hybrid vehicles (HV), and plugin hybrid vehicles (PHV).
It is known that decomposition of a nonaqueous electrolytic solution in a nonaqueous electrolytic solution secondary battery degrades the battery performance. The decomposition of nonaqueous electrolytic solutions occurs particularly easily during the overcharge. Accordingly, various techniques for suppressing the decomposition of nonaqueous electrolytic solutions during the overcharge have been developed.
For example, Japanese Patent Application Laid-open No. H10-154532 suggests including a phosphate compound in a positive electrode active material layer of a positive electrode of a nonaqueous electrolytic solution secondary battery. In Japanese Patent Application Laid-open No. H10-154532, it is indicated that as a result of including a phosphate compound such as lithium phosphate in the positive electrode active material layer, it is possible to suppress electrochemical decomposition of the electrolytic solution even during the battery overcharge.